I’ve never had to convert time to and from UTC. Recently had a request to have my app be timezone aware, and I’ve been running myself in circles. Lots of information on converting local time to UTC, which I found fairly elementary (maybe I’m doing that wrong as well), but I can not find any information on easily converting the UTC time to the end-users timezone.

In a nutshell, and android app sends me (appengine app) data and within that data is a timestamp. To store that timestamp to utc time I am using:

datetime.utcfromtimestamp(timestamp)

That seems to be working. When my app stores the data, it is being store as 5 hours ahead (I am EST -5)

The data is being stored on appengine’s BigTable, and when retrieved it comes out as a string like so:

"2011-01-21 02:37:21"

How do I convert this string to a DateTime in the users correct time zone?

Also, what is the recommended storage for a users timezone information? (How do you typically store tz info ie: “-5:00” or “EST” etc etc ?) I’m sure the answer to my first question might contain a parameter the answers the second.

If you don’t want to provide your own tzinfo objects, check out the python-dateutil library. It provides tzinfo implementations on top of a zoneinfo (Olson) database such that you can refer to time zone rules by a somewhat canonical name.

from datetime import datetime
from dateutil import tz

# METHOD 1: Hardcode zones:
from_zone = tz.gettz('UTC')
to_zone = tz.gettz('America/New_York')

# METHOD 2: Auto-detect zones:
from_zone = tz.tzutc()
to_zone = tz.tzlocal()

# utc = datetime.utcnow()
utc = datetime.strptime('2011-01-21 02:37:21', '%Y-%m-%d %H:%M:%S')

# Tell the datetime object that it's in UTC time zone since 
# datetime objects are 'naive' by default
utc = utc.replace(tzinfo=from_zone)

# Convert time zone
central = utc.astimezone(to_zone)

Edit Expanded example to show strptime usage

Edit 2 Fixed API usage to show better entry point method

Edit 3 Included auto-detect methods for timezones (Yarin)

Here’s a resilient method that doesn’t depend on any external libraries:

from datetime import datetime
import time

def datetime_from_utc_to_local(utc_datetime):
    now_timestamp = time.time()
    offset = datetime.fromtimestamp(now_timestamp) - datetime.utcfromtimestamp(now_timestamp)
    return utc_datetime + offset

This avoids the timing issues in DelboyJay’s example. And the lesser timing issues in Erik van Oosten’s amendment.

As an interesting footnote, the timezone offset computed above can differ from the following seemingly equivalent expression, probably due to daylight savings rule changes:

offset = datetime.fromtimestamp(0) - datetime.utcfromtimestamp(0) # NO!

Update: This snippet has the weakness of using the UTC offset of the present time, which may differ from the UTC offset of the input datetime. See comments on this answer for another solution.

To get around the different times, grab the epoch time from the time passed in. Here’s what I do:

def utc2local (utc):
    epoch = time.mktime(utc.timetuple())
    offset = datetime.fromtimestamp (epoch) - datetime.utcfromtimestamp (epoch)
    return utc + offset

See the datetime documentation on tzinfo objects. You have to implement the timezones you want to support yourself. The are examples at the bottom of the documentation.

Here’s a simple example:

from datetime import datetime,tzinfo,timedelta

class Zone(tzinfo):
    def __init__(self,offset,isdst,name):
        self.offset = offset
        self.isdst = isdst
        self.name = name
    def utcoffset(self, dt):
        return timedelta(hours=self.offset) + self.dst(dt)
    def dst(self, dt):
            return timedelta(hours=1) if self.isdst else timedelta(0)
    def tzname(self,dt):
         return self.name

GMT = Zone(0,False,'GMT')
EST = Zone(-5,False,'EST')

print datetime.utcnow().strftime('%m/%d/%Y %H:%M:%S %Z')
print datetime.now(GMT).strftime('%m/%d/%Y %H:%M:%S %Z')
print datetime.now(EST).strftime('%m/%d/%Y %H:%M:%S %Z')

t = datetime.strptime('2011-01-21 02:37:21','%Y-%m-%d %H:%M:%S')
t = t.replace(tzinfo=GMT)
print t
print t.astimezone(EST)

Output

01/22/2011 21:52:09 
01/22/2011 21:52:09 GMT
01/22/2011 16:52:09 EST
2011-01-21 02:37:21+00:00
2011-01-20 21:37:21-05:00a

If you want to get the correct result even for the time that corresponds to an ambiguous local time (e.g., during a DST transition) and/or the local utc offset is different at different times in your local time zone then use pytz timezones:

#!/usr/bin/env python
from datetime import datetime
import pytz    # $ pip install pytz
import tzlocal # $ pip install tzlocal

local_timezone = tzlocal.get_localzone() # get pytz tzinfo
utc_time = datetime.strptime("2011-01-21 02:37:21", "%Y-%m-%d %H:%M:%S")
local_time = utc_time.replace(tzinfo=pytz.utc).astimezone(local_timezone)

This answer should be helpful if you don’t want to use any other modules besides datetime.

datetime.utcfromtimestamp(timestamp) returns a naive datetime object (not an aware one). Aware ones are timezone aware, and naive are not. You want an aware one if you want to convert between timezones (e.g. between UTC and local time).

If you aren’t the one instantiating the date to start with, but you can still create a naive datetime object in UTC time, you might want to try this Python 3.x code to convert it:

import datetime

d=datetime.datetime.strptime("2011-01-21 02:37:21", "%Y-%m-%d %H:%M:%S") #Get your naive datetime object
d=d.replace(tzinfo=datetime.timezone.utc) #Convert it to an aware datetime object in UTC time.
d=d.astimezone() #Convert it to your local timezone (still aware)
print(d.strftime("%d %b %Y (%I:%M:%S:%f %p) %Z")) #Print it with a directive of choice

Be careful not to mistakenly assume that if your timezone is currently MDT that daylight savings doesn’t work with the above code since it prints MST. You’ll note that if you change the month to August, it’ll print MDT.

Another easy way to get an aware datetime object (also in Python 3.x) is to create it with a timezone specified to start with. Here’s an example, using UTC:

import datetime, sys

aware_utc_dt_obj=datetime.datetime.now(datetime.timezone.utc) #create an aware datetime object
dt_obj_local=aware_utc_dt_obj.astimezone() #convert it to local time

#The following section is just code for a directive I made that I liked.
if sys.platform=="win32":
    directive="%#d %b %Y (%#I:%M:%S:%f %p) %Z"
else:
    directive="%-d %b %Y (%-I:%M:%S:%f %p) %Z"

print(dt_obj_local.strftime(directive))

If you use Python 2.x, you’ll probably have to subclass datetime.tzinfo and use that to help you create an aware datetime object, since datetime.timezone doesn’t exist in Python 2.x.

If using Django, you can use the timezone.localtime method:

from django.utils import timezone
date 
# datetime.datetime(2014, 8, 1, 20, 15, 0, 513000, tzinfo=<UTC>)

timezone.localtime(date)
# datetime.datetime(2014, 8, 1, 16, 15, 0, 513000, tzinfo=<DstTzInfo 'America/New_York' EDT-1 day, 20:00:00 DST>)

You can use arrow

from datetime import datetime
import arrow

now = datetime.utcnow()

print(arrow.get(now).to('local').format())
# '2018-04-04 15:59:24+02:00'

you can feed arrow.get() with anything. timestamp, iso string etc

I traditionally defer this to the frontend — send times from the backend as timestamps or some other datetime format in UTC, then let the client figure out the timezone offset and render this data in the proper timezone.

For a webapp, this is pretty easy to do in javascript — you can figure out the browser’s timezone offset pretty easily using builtin methods and then render the data from the backend properly.

You can use calendar.timegm to convert your time to seconds since Unix epoch and time.localtime to convert back:

import calendar
import time

time_tuple = time.strptime("2011-01-21 02:37:21", "%Y-%m-%d %H:%M:%S")
t = calendar.timegm(time_tuple)

print time.ctime(t)

Gives Fri Jan 21 05:37:21 2011 (because I’m in UTC+03:00 timezone).

import datetime

def utc_str_to_local_str(utc_str: str, utc_format: str, local_format: str):
    """
    :param utc_str: UTC time string
    :param utc_format: format of UTC time string
    :param local_format: format of local time string
    :return: local time string
    """
    temp1 = datetime.datetime.strptime(utc_str, utc_format)
    temp2 = temp1.replace(tzinfo=datetime.timezone.utc)
    local_time = temp2.astimezone()
    return local_time.strftime(local_format)

utc = '2018-10-17T00:00:00.111Z'
utc_fmt = '%Y-%m-%dT%H:%M:%S.%fZ'
local_fmt = '%Y-%m-%dT%H:%M:%S+08:00'
local_string = utc_str_to_local_str(utc, utc_fmt, local_fmt)
print(local_string)   # 2018-10-17T08:00:00+08:00

for example, my timezone is ‘+08:00‘. input utc = 2018-10-17T00:00:00.111Z, then I will get output = 2018-10-17T08:00:00+08:00

From the answer here, you can use the time module to convert from utc to the local time set in your computer:

utc_time = time.strptime("2018-12-13T10:32:00.000", "%Y-%m-%dT%H:%M:%S.%f")
utc_seconds = calendar.timegm(utc_time)
local_time = time.localtime(utc_seconds)

Here is a quick and dirty version that uses the local systems settings to work out the time difference. NOTE: This will not work if you need to convert to a timezone that your current system is not running in. I have tested this with UK settings under BST timezone

from datetime import datetime
def ConvertP4DateTimeToLocal(timestampValue):
   assert isinstance(timestampValue, int)

   # get the UTC time from the timestamp integer value.
   d = datetime.utcfromtimestamp( timestampValue )

   # calculate time difference from utcnow and the local system time reported by OS
   offset = datetime.now() - datetime.utcnow()

   # Add offset to UTC time and return it
   return d + offset

Consolidating the answer from franksands into a convenient method.

import calendar
import datetime

def to_local_datetime(utc_dt):
    """
    convert from utc datetime to a locally aware datetime according to the host timezone

    :param utc_dt: utc datetime
    :return: local timezone datetime
    """
    return datetime.datetime.fromtimestamp(calendar.timegm(utc_dt.timetuple()))

How do I convert a datetime string in local time to a string in UTC time?

I’m sure I’ve done this before, but can’t find it and SO will hopefully help me (and others) do that in future.

Clarification: For example, if I have 2008-09-17 14:02:00 in my local timezone (+10), I’d like to generate a string with the equivalent UTC time: 2008-09-17 04:02:00.

Also, from http://lucumr.pocoo.org/2011/7/15/eppur-si-muove/, note that in general this isn’t possible as with DST and other issues there is no unique conversion from local time to UTC time.

First, parse the string into a naive datetime object. This is an instance of datetime.datetime with no attached timezone information. See documentation for datetime.strptime for information on parsing the date string.

Use the pytz module, which comes with a full list of time zones + UTC. Figure out what the local timezone is, construct a timezone object from it, and manipulate and attach it to the naive datetime.

Finally, use datetime.astimezone() method to convert the datetime to UTC.

Source code, using local timezone “America/Los_Angeles”, for the string “2001-2-3 10:11:12”:

import pytz, datetime
local = pytz.timezone ("America/Los_Angeles")
naive = datetime.datetime.strptime ("2001-2-3 10:11:12", "%Y-%m-%d %H:%M:%S")
local_dt = local.localize(naive, is_dst=None)
utc_dt = local_dt.astimezone(pytz.utc)

From there, you can use the strftime() method to format the UTC datetime as needed:

utc_dt.strftime ("%Y-%m-%d %H:%M:%S")

NOTE — As of 2020 you should not be using .utcnow() or .utcfromtimestamp(xxx). As you’ve presumably moved on to python3,you should be using timezone aware datetime objects.

>>> from datetime import timezone
>>> dt_now = datetime.now(tz=timezone.utc)
>>> dt_ts = datetime.fromtimestamp(1571595618.0, tz=timezone.utc)

for details see: see: https://blog.ganssle.io/articles/2019/11/utcnow.html

original answer (from 2010):

The datetime module’s utcnow() function can be used to obtain the current UTC time.

>>> import datetime
>>> utc_datetime = datetime.datetime.utcnow()
>>> utc_datetime.strftime("%Y-%m-%d %H:%M:%S")
'2010-02-01 06:59:19'

As the link mentioned above by Tom: http://lucumr.pocoo.org/2011/7/15/eppur-si-muove/ says:

UTC is a timezone without daylight saving time and still a timezone without configuration changes in the past.

Always measure and store time in UTC.

If you need to record where the time was taken, store that separately. Do not store the local time + timezone information!

NOTE – If any of your data is in a region that uses DST, use pytz and take a look at John Millikin’s answer.

If you want to obtain the UTC time from a given string and your lucky enough to be in a region in the world that either doesn’t use DST, or you have data that is only offset from UTC without DST applied:

–> using local time as the basis for the offset value:

>>> # Obtain the UTC Offset for the current system:
>>> UTC_OFFSET_TIMEDELTA = datetime.datetime.utcnow() - datetime.datetime.now()
>>> local_datetime = datetime.datetime.strptime("2008-09-17 14:04:00", "%Y-%m-%d %H:%M:%S")
>>> result_utc_datetime = local_datetime + UTC_OFFSET_TIMEDELTA
>>> result_utc_datetime.strftime("%Y-%m-%d %H:%M:%S")
'2008-09-17 04:04:00'

–> Or, from a known offset, using datetime.timedelta():

>>> UTC_OFFSET = 10
>>> result_utc_datetime = local_datetime - datetime.timedelta(hours=UTC_OFFSET)
>>> result_utc_datetime.strftime("%Y-%m-%d %H:%M:%S")
'2008-09-17 04:04:00'

UPDATE:

Since python 3.2 datetime.timezone is available. You can generate a timezone aware datetime object with the command below:

import datetime

timezone_aware_dt = datetime.datetime.now(datetime.timezone.utc)

If your ready to take on timezone conversions go read this:

https://medium.com/@eleroy/10-things-you-need-to-know-about-date-and-time-in-python-with-datetime-pytz-dateutil-timedelta-309bfbafb3f7

Thanks @rofly, the full conversion from string to string is as follows:

time.strftime("%Y-%m-%d %H:%M:%S", 
              time.gmtime(time.mktime(time.strptime("2008-09-17 14:04:00", 
                                                    "%Y-%m-%d %H:%M:%S"))))

My summary of the time/calendar functions:

time.strptime
string –> tuple (no timezone applied, so matches string)

time.mktime
local time tuple –> seconds since epoch (always local time)

time.gmtime
seconds since epoch –> tuple in UTC

and

calendar.timegm
tuple in UTC –> seconds since epoch

time.localtime
seconds since epoch –> tuple in local timezone

Here’s a summary of common Python time conversions.

Some methods drop fractions of seconds, and are marked with (s). An explicit formula such as ts = (d - epoch) / unit can be used instead (thanks jfs).

• struct_time (UTC) → POSIX (s):
  calendar.timegm(struct_time)
• Naïve datetime (local) → POSIX (s):
  calendar.timegm(stz.localize(dt, is_dst=None).utctimetuple())
  (exception during DST transitions, see comment from jfs)
• Naïve datetime (UTC) → POSIX (s):
  calendar.timegm(dt.utctimetuple())
• Aware datetime → POSIX (s):
  calendar.timegm(dt.utctimetuple())
• POSIX → struct_time (UTC, s):
  time.gmtime(t)
  (see comment from jfs)
• Naïve datetime (local) → struct_time (UTC, s):
  stz.localize(dt, is_dst=None).utctimetuple()
  (exception during DST transitions, see comment from jfs)
• Naïve datetime (UTC) → struct_time (UTC, s):
  dt.utctimetuple()
• Aware datetime → struct_time (UTC, s):
  dt.utctimetuple()
• POSIX → Naïve datetime (local):
  datetime.fromtimestamp(t, None)
  (may fail in certain conditions, see comment from jfs below)
• struct_time (UTC) → Naïve datetime (local, s):
  datetime.datetime(struct_time[:6], tzinfo=UTC).astimezone(tz).replace(tzinfo=None)
  (can’t represent leap seconds, see comment from jfs)
• Naïve datetime (UTC) → Naïve datetime (local):
  dt.replace(tzinfo=UTC).astimezone(tz).replace(tzinfo=None)
• Aware datetime → Naïve datetime (local):
  dt.astimezone(tz).replace(tzinfo=None)
• POSIX → Naïve datetime (UTC):
  datetime.utcfromtimestamp(t)
• struct_time (UTC) → Naïve datetime (UTC, s):
  datetime.datetime(*struct_time[:6])
  (can’t represent leap seconds, see comment from jfs)
• Naïve datetime (local) → Naïve datetime (UTC):
  stz.localize(dt, is_dst=None).astimezone(UTC).replace(tzinfo=None)
  (exception during DST transitions, see comment from jfs)
• Aware datetime → Naïve datetime (UTC):
  dt.astimezone(UTC).replace(tzinfo=None)
• POSIX → Aware datetime:
  datetime.fromtimestamp(t, tz)
  (may fail for non-pytz timezones)
• struct_time (UTC) → Aware datetime (s):
  datetime.datetime(struct_time[:6], tzinfo=UTC).astimezone(tz)
  (can’t represent leap seconds, see comment from jfs)
• Naïve datetime (local) → Aware datetime:
  stz.localize(dt, is_dst=None)
  (exception during DST transitions, see comment from jfs)
• Naïve datetime (UTC) → Aware datetime:
  dt.replace(tzinfo=UTC)

Source: taaviburns.ca

def local_to_utc(t):
    secs = time.mktime(t)
    return time.gmtime(secs)

def utc_to_local(t):
    secs = calendar.timegm(t)
    return time.localtime(secs)

Source: http://feihonghsu.blogspot.com/2008/02/converting-from-local-time-to-utc.html

Example usage from bd808: If your source is a datetime.datetime object t, call as:

local_to_utc(t.timetuple())

I’m having good luck with dateutil (which is widely recommended on SO for other related questions):

from datetime import *
from dateutil import *
from dateutil.tz import *

# METHOD 1: Hardcode zones:
utc_zone = tz.gettz('UTC')
local_zone = tz.gettz('America/Chicago')
# METHOD 2: Auto-detect zones:
utc_zone = tz.tzutc()
local_zone = tz.tzlocal()

# Convert time string to datetime
local_time = datetime.strptime("2008-09-17 14:02:00", '%Y-%m-%d %H:%M:%S')

# Tell the datetime object that it's in local time zone since 
# datetime objects are 'naive' by default
local_time = local_time.replace(tzinfo=local_zone)
# Convert time to UTC
utc_time = local_time.astimezone(utc_zone)
# Generate UTC time string
utc_string = utc_time.strftime('%Y-%m-%d %H:%M:%S')

(Code was derived from this answer to Convert UTC datetime string to local datetime)

One more example with pytz, but includes localize(), which saved my day.

import pytz, datetime
utc = pytz.utc
fmt = '%Y-%m-%d %H:%M:%S'
amsterdam = pytz.timezone('Europe/Amsterdam')

dt = datetime.datetime.strptime("2012-04-06 10:00:00", fmt)
am_dt = amsterdam.localize(dt)
print am_dt.astimezone(utc).strftime(fmt)
'2012-04-06 08:00:00'

I’ve had the most success with python-dateutil:

from dateutil import tz

def datetime_to_utc(date):
    """Returns date in UTC w/o tzinfo"""
    return date.astimezone(tz.gettz('UTC')).replace(tzinfo=None) if date.tzinfo else date

import time

import datetime

def Local2UTC(LocalTime):

    EpochSecond = time.mktime(LocalTime.timetuple())
    utcTime = datetime.datetime.utcfromtimestamp(EpochSecond)

    return utcTime

>>> LocalTime = datetime.datetime.now()

>>> UTCTime = Local2UTC(LocalTime)

>>> LocalTime.ctime()

'Thu Feb  3 22:33:46 2011'

>>> UTCTime.ctime()

'Fri Feb  4 05:33:46 2011'

if you prefer datetime.datetime:

dt = datetime.strptime("2008-09-17 14:04:00","%Y-%m-%d %H:%M:%S")
utc_struct_time = time.gmtime(time.mktime(dt.timetuple()))
utc_dt = datetime.fromtimestamp(time.mktime(utc_struct_time))
print dt.strftime("%Y-%m-%d %H:%M:%S")

Simple

I did it like this:

>>> utc_delta = datetime.utcnow()-datetime.now()
>>> utc_time = datetime(2008, 9, 17, 14, 2, 0) + utc_delta
>>> print(utc_time)
2008-09-17 19:01:59.999996

Fancy Implementation

If you want to get fancy, you can turn this into a functor:

class to_utc():
    utc_delta = datetime.utcnow() - datetime.now()

    def __call__(cls, t):
        return t + cls.utc_delta

Result:

>>> utc_converter = to_utc()
>>> print(utc_converter(datetime(2008, 9, 17, 14, 2, 0)))
2008-09-17 19:01:59.999996

You can do it with:

>>> from time import strftime, gmtime, localtime
>>> strftime('%H:%M:%S', gmtime()) #UTC time
>>> strftime('%H:%M:%S', localtime()) # localtime

How about –

time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime(seconds))

if seconds is None then it converts the local time to UTC time else converts the passed in time to UTC.

For getting around day-light saving, etc.

None of the above answers particularly helped me. The code below works for GMT.

def get_utc_from_local(date_time, local_tz=None):
    assert date_time.__class__.__name__ == 'datetime'
    if local_tz is None:
        local_tz = pytz.timezone(settings.TIME_ZONE) # Django eg, "Europe/London"
    local_time = local_tz.normalize(local_tz.localize(date_time))
    return local_time.astimezone(pytz.utc)

import pytz
from datetime import datetime

summer_11_am = datetime(2011, 7, 1, 11)
get_utc_from_local(summer_11_am)
>>>datetime.datetime(2011, 7, 1, 10, 0, tzinfo=<UTC>)

winter_11_am = datetime(2011, 11, 11, 11)
get_utc_from_local(winter_11_am)
>>>datetime.datetime(2011, 11, 11, 11, 0, tzinfo=<UTC>)

Using http://crsmithdev.com/arrow/

arrowObj = arrow.Arrow.strptime('2017-02-20 10:00:00', '%Y-%m-%d %H:%M:%S' , 'US/Eastern')

arrowObj.to('UTC') or arrowObj.to('local') 

This library makes life easy :)

I found the best answer on another question here. It only uses python built-in libraries and does not require you to input your local timezone (a requirement in my case)

import time
import calendar

local_time = time.strptime("2018-12-13T09:32:00.000", "%Y-%m-%dT%H:%M:%S.%f")
local_seconds = time.mktime(local_time)
utc_time = time.gmtime(local_seconds)

I’m reposting the answer here since this question pops up in google instead of the linked question depending on the search keywords.

I have this code in one of my projects:

from datetime import datetime
## datetime.timezone works in newer versions of python
try:
    from datetime import timezone
    utc_tz = timezone.utc
except:
    import pytz
    utc_tz = pytz.utc

def _to_utc_date_string(ts):
    # type (Union[date,datetime]]) -> str
    """coerce datetimes to UTC (assume localtime if nothing is given)"""
    if (isinstance(ts, datetime)):
        try:
            ## in python 3.6 and higher, ts.astimezone() will assume a
            ## naive timestamp is localtime (and so do we)
            ts = ts.astimezone(utc_tz)
        except:
            ## in python 2.7 and 3.5, ts.astimezone() will fail on
            ## naive timestamps, but we'd like to assume they are
            ## localtime
            import tzlocal
            ts = tzlocal.get_localzone().localize(ts).astimezone(utc_tz)
    return ts.strftime("%Y%m%dT%H%M%SZ")

In python3:

pip install python-dateutil

from dateutil.parser import tz

mydt.astimezone(tz.gettz('UTC')).replace(tzinfo=None) 

How about –

time.strftime("%Y-%m-%dT%H:%M:%SZ", time.gmtime(seconds))

if seconds is None then it converts the local time to UTC time else converts the passed in time to UTC.